Study On Aging Characteristics Of PVC Plastisol And The Cause Of "Pockmarks" In Its Products

The aging characteristics of plastisol prepared by PVC paste resin have obvious influence on its storage,processing and product properties.The aging characteristics of plastisol include various aging behaviors,which lead to the viscosity of plastisol changing constantly during aging.Viscosity stability in aging process is one of the most important indexes in processing.The properties of the products are mainly affected by the properties of plastisol and processing technology.In this paper,the aging characteristics of plastisol were studied from the aspects of the characteristics of PVC paste resin,the paste forming process and the aging behavior during the storage of plastisol.The relationship between the viscosity stability of plastisol and the above aspects was studied.The main causes of "pockmarks" and their effects on the mechanical properties of products were studied.The research contents mainly include the influence of the paste forming process on the viscosity stability of the plastisol,the influence of the properties of PVC paste resin on the aging behavior of the plastisol and the study of "pockmarks".The effect of paste forming process on viscosity stability of plastisol were studied by choosing two different agitators,the same agitator with different stirring rate and three different types of plasticizers.The results show that the plastisol prepared by planetary stirrer has better viscosity stability.The plastisol prepared by high speed disperser with medium stirring rate has lower viscosity and better viscosity stability,and the best defoaming performance.The oil absorption value of PVC paste resin with larger average particle size is lower,and it is easy to forming paste.The influence degree of three plasticizers on viscosity stability of plastisol is DOP > DOTP > DINP.Five kinds of PVC paste resins with different characteristics were selected to explore the influence of those characteristics on the aging behavior of plastisol.The effects of particle size distribution,particle morphology,secondary particle aggregation,real density and molecular weight on the viscosity stability and particle distribution uniformity of plastisol were studied.The results showed that the plastisol formed by the loose paste resin and the compact paste resin had lower initial viscosity.The loose secondary particles were more easily to disintegrate during the paste forming process,so the viscosity is stable.The plastisol formed by the compact paste resin still had large particles after 8 weeks of aging.And the particle distribution in the plastisol was uneven.In addition,the smaller the molecular weight is,the more obvious the swelling effect is.Finally,aiming at the problem of "pockmarks" commonly existed in PVC soft products.The plasticizing behavior of plastisol were studied and the cause of "pockmarks" were analyzed.The effect of vacuum defoaming and environmental humidity of plastisol on the number of "pockmarks" of plasticized films were studied,and the mechanical properties of each plasticized film were characterized.The effect of the number of "pockmarks" on the mechanical properties of plasticized films was studied.The results show that the number of " pockmarks" of the plasticized film prepared by the plastisol without vacuum defoaming is significantly higher than that prepared by vacuum defoaming under the same conditions.The breaking strength and elongation at break were significantly lower than that prepared by vacuum defoaming.The difference decreased significantly after aging for 2 days and disappeared after aging for 7 days.The number of " pockmarks" in the plasticized film,which prepared by plastisol aging for 7 days in the medium and high humidity environment,increased significantly with the increase of humidity.The elongation at break and breaking strength of the plasticized film decreased compared with those of the blank group.The number and mechanical properties of "pockmarks" in the plasticized film were nearly the same as those in the blank group after aging for 7 days in low humidity environment.